Monolithic Silicon Photomultiplier Array

ABSTRACT

An optical system may include a substrate and a plurality of silicon photomultipliers (SiPMs) monolithically integrated with the substrate. Each SiPM may include a plurality of single photon avalanche diodes (SPADs). The optical system also includes an aperture array having a plurality of apertures. The plurality of SiPMs and the aperture array are aligned so as to define a plurality of receiver channels. Each receiver channel includes a respective SiPM of the plurality of SiPMs optically coupled to a respective aperture of the plurality of apertures.

BACKGROUND

Optical systems (e.g., LIDAR devices) may include several elements, suchas light sources, optical elements, and/or photodetectors disposedwithin a common package. Furthermore, some elements of an optical systemmay be coupled to a common substrate.

SUMMARY

The present disclosure generally relates to optical systems (e.g., LIDARsystems) and certain aspects of their associated receiver subsystems.

In a first aspect, an optical system is provided. The optical systemincludes a substrate and a plurality of silicon photomultipliers (SiPMs)monolithically integrated with the substrate. Each SiPM includes aplurality of single photon avalanche diodes (SPADs). The optical systemalso includes an aperture array having a plurality of apertures. Theplurality of SiPMs and the aperture array are aligned so as to define aplurality of receiver channels. Each receiver channel includes arespective SiPM of the plurality of SiPMs optically coupled to arespective aperture of the plurality of apertures.

In a second aspect, a method of manufacturing an optical system isprovided. The method includes providing a monolithic SiPM array having aplurality of silicon photomultipliers (SiPMs) monolithically integratedwith a substrate. Each SiPM includes a plurality of single photonavalanche diodes (SPADs). The method additionally includes aligning anaperture array having a plurality of apertures with the monolithic SiPMarray so as to define a plurality of receiver channels. Each receiverchannel includes a respective SiPM of the plurality of SiPMs opticallycoupled to a respective aperture of the plurality of apertures.

Other aspects, embodiments, and implementations will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic block representation of an opticalsystem, according to an example embodiment.

FIG. 2A illustrates a cross-sectional view of an optical system,according to an example embodiment.

FIG. 2B illustrates a cross-sectional view of an optical system,according to an example embodiment.

FIG. 2C illustrates a top view of an optical system, according to anexample embodiment.

FIG. 3A illustrates a step of a method of manufacture, according to anexample embodiment.

FIG. 3B illustrates a step of a method of manufacture, according to anexample embodiment.

FIG. 3C illustrates a step of a method of manufacture, according to anexample embodiment.

FIG. 3D illustrates a step of a method of manufacture, according to anexample embodiment.

FIG. 4 illustrates a method, according to an example embodiment.

DETAILED DESCRIPTION

Example methods, devices, and systems are described herein. It should beunderstood that the words “example” and “exemplary” are used herein tomean “serving as an example, instance, or illustration.” Any embodimentor feature described herein as being an “example” or “exemplary” is notnecessarily to be construed as preferred or advantageous over otherembodiments or features. Other embodiments can be utilized, and otherchanges can be made, without departing from the scope of the subjectmatter presented herein.

Thus, the example embodiments described herein are not meant to belimiting. Aspects of the present disclosure, as generally describedherein, and illustrated in the figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are contemplated herein.

Further, unless context suggests otherwise, the features illustrated ineach of the figures may be used in combination with one another. Thus,the figures should be generally viewed as component aspects of one ormore overall embodiments, with the understanding that not allillustrated features are necessary for each embodiment.

I. Overview

An optical system (e.g., a LIDAR device) could include a plurality ofreceiver channels. In example scenarios, each receiver channel includesa pinhole aligned over a discrete silicon photomultiplier (SiPM). Thepinhole can reduce detection of ambient light. Each SiPM includes aplurality of (e.g., over 2000) single photon avalanche diodes (SPADs)electrically-connected together (e.g., connected in parallel). A SPAD isa single-photon sensitive device that is designed to operate in Geigermode. In some embodiments, an optical system could include over 200receiver channels (arranged in two groups of over 100 receiver channelseach). In such cases, fabrication of the plurality of receiver channelsmay involve mounting over 200 individual SiPMs to one or more printedcircuit boards (PCBs).

Fabrication of the optical system can be improved by providing amonolithic SiPM array in which multiple SiPMs are formed on a singlesubstrate (e.g., a silicon wafer). Each SiPM on the substrate can fillup a circular area that includes the same number ofelectrically-connected SPADs as is used (e.g., over 2000 per SiPM). Insuch a scenario, if the circular SiPMs are arranged in a hexagonal orsquare array with a density of between 0.2 and 0.6 SiPMs per mm² (e.g.,about 0.4 SiPMs per mm²), it may be feasible to fit about 200 SiPMs on a1-inch diameter silicon wafer. In this way, four silicon substrates withrespective monolithic SiPM arrays could be utilized to provide acomparable number of SiPMs as that used in the contemporary opticalsystem design.

With multiple SiPMs monolithically integrated onto the same substrate,it is desirable to include structures that provide electrical and/oroptical isolation between SiPMs (e.g., to reduce cross-talk betweenadjacent SiPMs). In one approach, each SiPM may be surrounded by a deeptrench in the substrate that is filled in with a metal or anotheroptically opaque, conductive, and/or non-conductive material. The filledtrenches can block photo-generated electrons from a SiPM from reachingan adjacent SiPM (electrical isolation) and can also block photons froma SiPM from reaching an adjacent SiPM (optical isolation). To provideadditional optical isolation, a baffle structure can be positionedbetween the monolithic SiPM array and its corresponding pinhole array.In one approach, the baffle structure can include an array of holesdrilled or otherwise formed in an opaque material (e.g., metal orplastic), with each hole defining an optical path between a pinhole andits corresponding SiPM in the monolithic SiPM array. Further, each holecan have a diameter that matches the diameter of the SiPM. The bafflestructure can be attached to the monolithic SiPM array with the array ofholes aligned with the array of SiPMs, and the pinhole array can beattached to the baffle structure so that the pinholes are centered overthe holes. With this configuration, the light received through eachpinhole can reach the corresponding SiPM through the corresponding holein the baffle structure but is blocked by the opaque material fromreaching adjacent SiPMs.

Electrical contacts for the monolithic array can be provided indifferent ways. In one approach, electrical contacts could be providedon the backside of the substrate. Alternatively, electrical contactscould be provided from the side and/or routed along a top surface of thesubstrate.

Other aspects, embodiments, and implementations will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings.

II. Example Systems

FIG. 1 illustrates a schematic block representation of an optical system100, according to an example embodiment. In some cases, optical system100 could be utilized as a portion of a LIDAR system, such as a receiversubsystem of the LIDAR system. The LIDAR system may be coupled to avehicle and used in the operation of the vehicle, such as when thevehicle is in an autonomous or semi-autonomous mode or when the vehicleis a fully autonomous vehicle. A vehicle may be, for example, a car,truck, tractor-trailer, construction equipment such as bulldozers, anautonomous drone aircraft, or a robot such as a sidewalk delivery robot.Such LIDAR systems may be configured to provide information (e.g., pointcloud data) about one or more objects (e.g., location, shape, etc.) in agiven environment. In an example embodiment, the LIDAR system couldprovide point cloud information, object information, mappinginformation, or other information to a vehicle. Other types of vehiclesand LIDAR systems are contemplated herein.

The optical system 100 includes a substrate 110, which includes a firstsurface 112 and a second surface 114.

In some examples, the substrate 110 could be approximately 200 micronsthick. For instance, the substrate 110 could have a thickness of between100 to 500 microns. However, other thicknesses are possible andcontemplated. In some embodiments, the substrate 110 could include asemiconductor substrate material such as a silicon substrate (e.g., asilicon wafer), an indium phosphide substrate (e.g., an indium phosphidewafer), a gallium arsenide substrate (e.g., a GaAs wafer), or the like.In an example embodiment, the substrate 110 could include a silicongermanium-on-silicon substrate. In some embodiments, the substrate 110could include a silicon-on-insulator (SOI) material. Alternatively, thesubstrate 110 could be formed from a variety of other solid and/orflexible materials, each of which is contemplated in the presentdisclosure.

The optical system 100 includes a plurality of silicon photomultiplier(SiPM) devices 120 that are monolithically integrated with the substrate110. Each of the SiPM devices 120 may constitute a plurality of singlephoton avalanche diodes (SPADs) 122. For example, each SiPM of theplurality of SiPMs 120 could include at least 1000 SPADs 122. It will beunderstood that more or less SPADs 122 could be associated with eachSiPM of the plurality of SiPMs 120.

In some embodiments, the plurality of SiPMs 120 could be arranged alongthe substrate in a hexagonal or square array. That is, each SiPM of theplurality of SiPMs 120 could be arranged at a respective lattice pointof a hexagonal, triangular, or a square lattice. Other close-packingarrangements of the respective SiPMs in the plurality of SiPMs 120 arepossible and contemplated. In some embodiments, the SiPMs of theplurality of SiPMs are arranged along the substrate with a density ofbetween 0.2 to 0.6 SiPMs per mm² (e.g., about 0.4 SiPMs per mm²). Itwill be understood that higher or lower densities of SiPMs per mm² arecontemplated and possible. While SiPMs are described in relation to someembodiments of the present disclosure, other types of photo-sensitivedetector devices are possible.

The optical system 100 further includes an aperture array 130, whichincludes a plurality of apertures 132. The plurality of SiPM devices 120and the aperture array 130 are aligned so as to define a plurality ofreceiver channels 140. In such scenarios, each receiver channel 140includes a respective SiPM of the plurality of SiPM devices 120 beingoptically coupled to a respective aperture of the plurality of apertures132.

In some embodiments, the optical system 100 includes a plurality ofelectrical conductors 150. For example, the plurality of electricalconductors may be coupled to the plurality of SiPMs 120 via at least oneof: a through substrate via (TSV) or a side routing arrangement. Otherways to route the electrical conductors 150 are contemplated andpossible. For example, the plurality of electrical conductors 150 couldbe connected to other circuitry by way of a top-level wire bondconnection. Additionally or alternatively, the electrical conductors 150could be routed along spaces between the SiPM devices 120 (e.g., in the“streets” between SiPM devices).

Furthermore, the optical system 100 includes isolation trenches 116. Theisolation trenches 116 could be located in the substrate 110. In someembodiments, the isolation trenches 116 could be arranged betweenneighboring SiPMs of the plurality of SiPM devices 120. At least one ofthe isolation trenches 116 may be at least partially filled with fillmaterial 118. For example, the at least one isolation trench 116 couldbe at least partially filled with at least one of: a metal material, anoptically-opaque material, a conductive material, or a non-conductivematerial. In such scenarios, the at least one isolation trench 116provides electrical isolation between the neighboring SiPMs of theplurality of SiPM devices 120.

Additionally or alternatively, in some embodiments, the at least oneisolation trench 11 could provide optical isolation between theneighboring SiPMs of the plurality of SiPM devices 120.

In some embodiments, the optical system 100 includes a baffle structure160. The baffle structure 160 includes a plurality of openings 162 in anoptically opaque material. In such scenarios, the baffle structure 160is arranged between the aperture array 130 and the plurality of SiPMs120 such that each receiver channel 140 includes a respective SiPM ofthe plurality of SiPMs 120 that is optically coupled to a respectiveaperture of the plurality of apertures 132 via a respective opening inthe baffle structure 160.

In some embodiments, a cross-section of the baffle structure 160 couldinclude a plurality of diamond-shaped members separated by therespective openings in the baffle structure 160.

FIG. 2A illustrates a cross-sectional view of an optical system 200,according to an example embodiment. FIG. 2A could include elements thatare similar or identical to those of optical system 100 illustrated anddescribed in reference to FIG. 1. FIG. 2A is meant to illustrate thegeneral arrangement of the elements of optical system 200 and notnecessarily meant to show the exact scale or proportion of suchelements.

In some embodiments, the optical system 200 could include a substrate110 with a first surface 112 and a second surface 114. As illustrated,the first surface 112 could be arranged opposite the second surface 114.As described elsewhere, substrate 110 could include a semiconductorsubstrate (e.g., a semiconductor wafer). For instance, the first surface112 could include a top surface of a silicon wafer and the secondsurface 114 could include a bottom surface of the silicon wafer.

As illustrated in FIG. 2A, the optical system 200 could include aplurality of silicon photomultiplier (SiPM) devices 120 (e.g., SiPMs 120a, 120 b, 120 c, and 120 d) that are monolithically integrated with thesubstrate 110. That is, the SiPMs 120 a, 120 b, 120 c, and 120 d couldbe formed, at least in part, within the substrate 110. For example, theSiPMs 120 a, 120 b, 120 c, and 120 d could each include a plurality ofSPADs. SPADs are semiconductor devices that include a p-n junction thatis designed to operate when reverse-biased at a voltage V_(a) greaterthan a breakdown voltage V_(B) of the junction. For example, V_(a) couldbe applied across the p-n junction, which could be approximately 1-5microns thick, so as to provide an electric field greater than 3×10⁵V/cm. Other electric fields are possible and contemplated.

In some embodiments, the SPADs 122 could be configured to detectinfrared light (e.g., 905 nm or 1550 nm). However, other wavelengths oflight could be detected as well.

The SPADs 122 could be configured and/or biased so as to provide amilliampere or more of photocurrent in response to absorbing a singlephoton. Other configurations and/or photocurrents are possible andcontemplated.

In some embodiments, the SPADs could include a passive or activequenching circuit. For example, the passive quenching circuit couldinclude a resistor coupled in series with the SPAD. Additionally oralternatively, the active quenching circuit could include a fastdiscriminator circuit or a synchronous bias voltage reduction circuit.

In some embodiments, each SiPM of the plurality of SiPMs 120 couldinclude at least 1000 SPADs 122. It will be understood that more or lessSPADs 122 could be associated with each SiPM of the plurality of SiPMs120.

In some embodiments, SiPMs 120 a, 120 b, 120 c, and 120 d could beseparated by a respective plurality of isolation trenches 116. Theisolation trenches 116 could be formed by utilizing alithographically-defined wet or dry etch process. Other semiconductormanufacturing techniques to form the isolation trenches 116 are possibleand contemplated. Some or all of the isolation trenches 116 could befilled, at least partially, by fill material 118.

As illustrated in FIG. 2A, electrical conductors 150 could be locatedalong the first surface 112 (e.g., along a periphery of the respectiveSiPMs 120 a, 120 b, 120 c, and 120 d. Additionally or alternatively,electrical conductor 150 could be coupled to the second surface 114. Itwill be understood that electrical conductor 150 could be located inother positions so as to electrically couple the respective SiPMs 120 a,120 b, 120 c, and 120 d to detection circuitry. Other ways to physicallyand/or electrically connect the respective SiPMs 120 a, 120 b, 120 c,and 120 d to detection circuitry are possible and contemplated, such as,without limitation, conventional solder balls, ball-grid arrays (BGA),land-grid arrays (LGA), conductive paste, and other types of physicaland electrical sockets.

In some embodiments, the diamond-shaped members of the baffle structure160 could be arranged so as to optically isolate the receiver channels140 a, 140 b, 140 c, and 140 d from one another. For example, the bafflestructure 160 could provide an opaque barrier between respectivereceiver channels. The diamond-shaped portions of the baffle structure160 could be physically coupled between the fill material 118 andaperture array 130. Between the diamond-shaped portions of the bafflestructure 160, light may be directed toward the respective SiPMs 120 a,120 b, 120 c, and 120 d by way of the respective openings 162 a, 162 b,162 c, and 162 d.

In example embodiments, the aperture array 130 could include apertures132 a-132 d, which could each have an open diameter of 120-160 microns.However, other aperture diameters are possible and contemplated. Theplurality of apertures 132 a-132 d could include holes drilled orlithographically etched through a material that is substantially opaqueto light. In other embodiments, the plurality of apertures 132 a-132 dcould include optical windows that are substantially transparent tolight.

Additionally or alternatively, other ways are contemplated and possibleto optically isolate adjacent SiPMs. For example, a reflective gridcould be patterned along a top surface of the SiPMs. The reflective gridcould be formed from metal or another optically opaque material. Thereflective grid could be defined so as to align with the bafflestructure 160 and/or the aperture array 130. In such a scenario, lightfalling between adjacent SiPM devices would not enter the siliconsubstrate. Such optical isolation could reduce inter-channel crosstalkat the potential expense of slightly reducing fill factor for a givenSiPM array.

Furthermore, in some embodiments, the aperture array 130 and bafflestructure 160 could be replaced by a combination aperture/bafflestructure. Such a combination structure could include a thick opaqueplate with deep holes, drilled or etched to correspond with SiPM devicelocations.

In lieu of, or in combination with the aperture array 130 and bafflestructure 160, some embodiments could include a set of vertical,optically-transparent pillars (e.g., optical waveguides) that may serveas a lightguide and couple light to the SiPM devices using totalinternal reflection. FIG. 2B illustrates a cross-sectional view of anoptical system 220, according to an example embodiment. As illustratedin FIG. 2B, optical system 220 could include optical waveguides 222 a,222 b, 222 c, and 222 d, which could be configured to guide light towardthe respective SiPM devices 120 a, 120 b, 120 c, and 120 d. Asillustrated, the optical waveguides 222 a, 222 b, 222 c, and 222 d couldhave a tapered shape. In other examples, the optical waveguides 222 a,222 b, 222 c, and 222 d could have a straight sidewall and/or take onanother shape. In some scenarios, an “active isolation region” could bedefined by growing dielectric stacks 224 a, 224 b, 224 c, and 224 d overthe respective SiPM devices 120 a, 120 b, 120 c, and 120 d. Thedielectric stacks 224 a, 224 b, 224 c, and 224 d could be configured tocouple light from the optical waveguides 222 a, 222 b, 222 c, and 222 dinto the respective SiPM devices 120 a, 120 b, 120 c, and 120 d. In someembodiments, further optical isolation between SiPM devices 120 a, 120b, 120 c, and 120 d could be achieved by etching the dielectric stackbetween SiPM devices and then filling the trenches with anorganosiloxane-based planarizing material 226 (e.g., Silecs XC400L orthe like). In some embodiments, the planarizing material 226 could havea high refractive index relative to the optical waveguides 222 a, 222 b,222 c, and 222 d and/or the dielectric stacks 224 a, 224 b, 224 c, and224 d.

FIG. 2C illustrates a top view 250 of the optical system 200, accordingto an example embodiment. As illustrated in FIG. 2C, a plurality of SiPMdevices 120 could be arranged in a hexagonal array along a surface of asubstrate 110. Furthermore, the SiPM devices of the plurality of SiPMdevices 120 could be electrically and/or optically isolated from oneanother by way of one or more isolation trenches 116. In someembodiments, the isolation trenches 116 could be filled with a fillmaterial, as described herein.

It will be understood that various ways could be utilized toelectrically and/or optically isolate SiPM devices from one another. Forexample, while FIG. 2C illustrates a regular hexagonal array, variablespacing and/or variable isolation depths could be utilized betweenrespective receiver channels. For example, in reference to FIG. 2A,receiver channels 140 a, 140 b, 140 c, and 140 d could be isolated bytrenches have a first depth (e.g., 1 micron) between some receiverchannels and a second depth (e.g., 2 microns) between others.Furthermore, some receiver channels could be spaced further apart fromsome adjacent receiver channels than for others.

III. Example Methods

FIGS. 3A-3D illustrate various steps of a method of manufacture,according to one or more example embodiments. It will be understood thatat least some of the various steps may be carried out in a differentorder than of that presented herein. Furthermore, steps may be added,subtracted, transposed, and/or repeated. FIGS. 3A-3D may serve asexample illustrations for at least some of the steps or blocks describedin relation to method 400 as illustrated and described in relation toFIG. 4. Additionally, some steps of FIGS. 3A-3D may be carried out so asto provide optical system 100 and/or optical systems 200 or 220, asillustrated and described in reference to FIGS. 1, 2A, and 2B,respectively.

FIG. 3A illustrates a step of a method of manufacture 300, according toan example embodiment. Step 300 initially includes providing a substrate110. The substrate 110 may include a first surface 112 and a secondsurface 114. The substrate 110 could include a semiconductor material,such as a silicon or silicon-on-insulator substrate.

Step 300 could subsequently include forming a plurality of SiPMs 120 a,120 b, 120 c, and 120 d. In some embodiments, forming the plurality ofSiPMs 120 a, 120 b, 120 c, and 120 d could include forming p-n junctionsin the first surface 112. That is, the SiPMs 120 a, 120 b, 120 c, and120 d could be monolithically integrated with the substrate 110. EachSiPM includes a plurality of single photon avalanche diodes (SPADs). Insome embodiments, the plurality of SiPMs in the monolithic SiPM arraycould be arranged in a hexagonal or square array. In such scenarios, theplurality of SiPMs in the monolithic SiPM array could be arranged with adensity of about 0.4 SiPMs per mm².

Step 300 could additionally include forming a plurality of isolationtrenches 116 in the first surface 112 of the substrate 110. In someembodiments, forming the plurality of isolation trenches 116 couldinclude etching into the first surface 112 with a wet or dry etchprocess. Additionally or alternatively, the isolation trenches 116 couldbe formed by grinding, polishing, or another mechanical method. In someembodiments, the isolation trenches 116 could be arranged betweenneighboring SiPMs.

Step 300 could further include filling at least a portion of theisolation trenches 116 with a fill material 118. The isolation trenches116 could be at least partially filled with at least one of: a metalmaterial, an optically-opaque material, a conductive material, or anon-conductive material. As an example, the fill material 118 could bedeposited using a chemical vapor deposition process or an oxidationprocess. The at least one isolation trench could provide electricalisolation between the neighboring SiPMs. Additionally or alternatively,the at least one isolation trench could provide optical isolationbetween the neighboring SiPMs.

FIG. 3B illustrates a step of a method of manufacture 310, according toan example embodiment. Step 310 includes forming one or more electricalconductors 150 on a first surface 112 and/or a second surface 114 of thesubstrate 110. The electrical conductors 150 could provide electricalcoupling between the SiPMs 120 a, 120 b, 120 c, and 120 d and respectivedetection circuitry.

FIG. 3C illustrates a step of a method of manufacture 320, according toan example embodiment. Step 320 includes positioning a baffle structure160 comprising a plurality of openings 162 a, 162 b, 162 c, and 162 d inan optically opaque material. The baffle structure 160 could bepositioned so as to align a plurality of diamond-shaped structures witha plurality of isolation trenches 116 and/or the respective SiPMs 120 a,120 b, 120 c, and 120 d.

In some embodiments, the baffle structure 160 could be positionedbetween the monolithic SiPM array 120 a, 120 b, 120 c, and 120 d and theaperture array 130, as described herein. In some embodiments, the bafflestructure 160 could be positioned with a pick-and-place tool and couldbe aligned to underlying structures based on registration marks locatedalong the first surface 112.

FIG. 3D illustrates a step of a method of manufacture 330, according toan example embodiment. Step 330 includes aligning an aperture array 130with respect to the baffle structure 160 and/or the SiPMs 120 a, 120 b,120 c, and 120 d so as to define a plurality of receiver channels (e.g.,receiver channels 140 a, 140 b, 140 c, and 140 d as illustrated anddescribed in reference to FIG. 2A). The aperture array 130 includes aplurality of apertures 132 a, 132 b, 132 c, and 132 d. Each receiverchannel includes a respective SiPM of the plurality of SiPMs opticallycoupled to a respective aperture of the plurality of apertures and arespective opening in the baffle structure.

FIG. 4 illustrates a method 400, according to an example embodiment.Method 400 may be carried out, at least in part, by way of some or allof the manufacturing steps or stages illustrated and described inreference to FIGS. 3A-3D. It will be understood that the method 400 mayinclude fewer or more steps or blocks than those expressly disclosedherein. Furthermore, respective steps or blocks of method 400 may beperformed in any order and each step or block may be performed one ormore times. In some embodiments, method 400 and its steps or blocks maybe performed to provide an optical system that could be similar oridentical to optical system 100 and/or optical system 200, asillustrated and described in reference to FIGS. 1 and 2.

Block 402 includes providing a monolithic SiPM array that includes aplurality of silicon photomultipliers (SiPMs) monolithically integratedwith a substrate. Each SiPM includes a plurality of single photonavalanche diodes (SPADs). In some embodiments, the plurality of SiPMs inthe monolithic SiPM array could be arranged in a hexagonal or squarearray. In such scenarios, the plurality of SiPMs in the monolithic SiPMarray could be arranged with a density of about 0.4 SiPMs per mm².

In some embodiments, the monolithic SiPM array further includes at leastone isolation trench in the substrate, wherein the at least oneisolation trench is arranged between neighboring SiPMs. Additionally oralternatively, the at least one isolation trench could be at leastpartially filled with at least one of: a metal material, anoptically-opaque material, a conductive material, or a non-conductivematerial.

In some examples, the at least one isolation trench could provideelectrical isolation between the neighboring SiPMs. Additionally oralternatively, the at least one isolation trench could provide opticalisolation between the neighboring SiPMs.

Block 404 includes aligning an aperture array having a plurality ofapertures with the monolithic SiPM array so as to define a plurality ofreceiver channels. Each receiver channel includes a respective SiPM ofthe plurality of SiPMs optically coupled to a respective aperture of theplurality of apertures.

In some embodiments, method 400 could further include positioning abaffle structure between the monolithic SiPM array and the aperturearray. In some scenarios, the baffle structure could include a pluralityof openings in an optically opaque material. Positioning the bafflestructure could be performed such that each receiver channel isassociated with a respective SiPM of the plurality of SiPMs beingoptically coupled to a respective aperture of the plurality of aperturesvia a respective opening in the baffle structure.

The particular arrangements shown in the Figures should not be viewed aslimiting. It should be understood that other embodiments may includemore or less of each element shown in a given Figure. Further, some ofthe illustrated elements may be combined or omitted. Yet further, anillustrative embodiment may include elements that are not illustrated inthe Figures.

A step or block that represents a processing of information cancorrespond to circuitry that can be configured to perform the specificlogical functions of a herein-described method or technique.Alternatively or additionally, a step or block that represents aprocessing of information can correspond to a module, a segment, aphysical computer (e.g., a field programmable gate array (FPGA) orapplication-specific integrated circuit (ASIC)), or a portion of programcode (including related data). The program code can include one or moreinstructions executable by a processor for implementing specific logicalfunctions or actions in the method or technique. The program code and/orrelated data can be stored on any type of computer readable medium suchas a storage device including a disk, hard drive, or other storagemedium.

The computer readable medium can also include non-transitory computerreadable media such as computer-readable media that store data for shortperiods of time like register memory, processor cache, and random accessmemory (RAM). The computer readable media can also includenon-transitory computer readable media that store program code and/ordata for longer periods of time. Thus, the computer readable media mayinclude secondary or persistent long term storage, like read only memory(ROM), optical or magnetic disks, compact-disc read only memory(CD-ROM), for example. The computer readable media can also be any othervolatile or non-volatile storage systems. A computer readable medium canbe considered a computer readable storage medium, for example, or atangible storage device.

While various examples and embodiments have been disclosed, otherexamples and embodiments will be apparent to those skilled in the art.The various disclosed examples and embodiments are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims.

What is claimed is:
 1. An optical system comprising: a substrate; aplurality of silicon photomultipliers (SiPMs) monolithically integratedwith the substrate, wherein each SiPM comprises a plurality of singlephoton avalanche diodes (SPADs); and an aperture array comprising aplurality of apertures, wherein the plurality of SiPMs and the aperturearray are aligned so as to define a plurality of receiver channels,wherein each receiver channel comprises a respective SiPM of theplurality of SiPMs optically coupled to a respective aperture of theplurality of apertures.
 2. The optical system of claim 1, wherein thesubstrate comprises a silicon wafer, an indium phosphide wafer, or agallium arsenide wafer.
 3. The optical system of claim 1, wherein eachSiPM of the plurality of SiPMs comprises at least 1000 SPADs.
 4. Theoptical system of claim 1, wherein the plurality of SiPMs are arrangedalong the substrate in a hexagonal or square array.
 5. The opticalsystem of claim 1, wherein the plurality of SiPMs are arranged along thesubstrate with a density of about 0.4 SiPMs per mm².
 6. The opticalsystem of claim 1, further comprising a plurality of electricalconductors, wherein the plurality of electrical conductors is coupled tothe plurality of SiPMs via at least one of: a through substrate via(TSV) or a side routing arrangement.
 7. The optical system of claim 1,further comprising at least one isolation trench in the substrate,wherein the at least one isolation trench is arranged betweenneighboring SiPMs.
 8. The optical system of claim 7, wherein the atleast one isolation trench is at least partially filled with at leastone of: a metal material, an optically-opaque material, a conductivematerial, or a non-conductive material.
 9. The optical system of claim7, wherein the at least one isolation trench provides electricalisolation or optical isolation between the neighboring SiPMs.
 10. Theoptical system of claim 1, further comprising a plurality of opticalwaveguides, wherein each optical waveguide is configured to couple lightinto a respective SiPM of the plurality of SiPMs.
 11. The optical systemof claim 1, further comprising: a baffle structure, wherein the bafflestructure comprises a plurality of openings in an optically opaquematerial, wherein the baffle structure is arranged between the aperturearray and the plurality of SiPMs such that each receiver channelcomprises a respective SiPM of the plurality of SiPMs optically coupledto a respective aperture of the plurality of apertures via a respectiveopening in the baffle structure.
 12. The optical system of claim 11,wherein a cross-section of the baffle structure comprises a plurality ofdiamond-shaped members separated by the respective openings in thebaffle structure.
 13. A method of manufacturing an optical system, themethod comprising: providing a monolithic SiPM array comprising aplurality of silicon photomultipliers (SiPMs) monolithically integratedwith a substrate, wherein each SiPM comprises a plurality of singlephoton avalanche diodes (SPADs); and aligning an aperture arraycomprising a plurality of apertures with the monolithic SiPM array so asto define a plurality of receiver channels, wherein each receiverchannel comprises a respective SiPM of the plurality of SiPMs opticallycoupled to a respective aperture of the plurality of apertures.
 14. Themethod of claim 13, wherein the plurality of SiPMs in the monolithicSiPM array are arranged in a hexagonal or square array.
 15. The methodof claim 13, wherein the plurality of SiPMs in the monolithic SiPM arrayare arranged with a density of about 0.4 SiPMs per mm².
 16. The methodof claim 13, wherein the monolithic SiPM array further comprises atleast one isolation trench in the substrate, wherein the at least oneisolation trench is arranged between neighboring SiPMs.
 17. The methodof claim 16, wherein the at least one isolation trench is at leastpartially filled with at least one of: a metal material, anoptically-opaque material, a conductive material, or a non-conductivematerial.
 18. The method of claim 16, wherein the at least one isolationtrench provides electrical isolation between the neighboring SiPMs. 19.The method of claim 16, wherein the at least one isolation trenchprovides optical isolation between the neighboring SiPMs.
 20. The methodof claim 13, further comprising: positioning a baffle structurecomprising a plurality of openings in an optically opaque materialbetween the monolithic SiPM array and the aperture array such that eachreceiver channel comprises a respective SiPM of the plurality of SiPMsoptically coupled to a respective aperture of the plurality of aperturesvia a respective opening in the baffle structure.